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Dynamics and synchrotron emission from radio-loud AGN

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Turner, RJ ORCID: 0000-0002-4376-5455 2018 , 'Dynamics and synchrotron emission from radio-loud AGN', PhD thesis, University of Tasmania.

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Abstract

I present a new analytical model describing the dynamics and luminosity evolution of Fanaroff-Riley type I and II radio active galactic nuclei (AGN), and the transition between these classes. The galaxy environments of a volume-limited low redshift (0:03 ≤ z ≤ 0:1) sample of observed AGN are quantifed using a semi-analytic galaxy formation model, and the model applied to these objects to determine their distribution of jet powers and active lifetimes at the present epoch. This technique is refined for radio sources in the 3C survey with multi-frequency spectral coverage by including a constraint on the magnetic field strength. Further, the ability of the model to correct for selection biases in future surveys is investigated by performing detailed modelling of the spatial distribution of synchrotron electrons within the radio lobes. Finally, I apply the model to simulated and observed extended radio galaxies to construct standardisable candles.
Results of this AGN evolution model show that radio sources in massive galaxies remain active for longer, spend less time in the quiescent phase, and inject more energy into their hosts than their less massive counterparts. The jet power is independent of the host stellar mass within model uncertainties, consistent with the maintenancemode AGN feedback paradigm. The environments of these AGN are in or close to long-term heating-cooling balance. I also examine the properties of high- and lowexcitation radio galaxy sub-populations. The HERGs are younger than LERGs by an order of magnitude, whilst their jet powers are greater by a factor of four on average. The Eddington-scaled accretion rates and jet production effciencies of these populations are consistent with LERGs being powered by radiatively ineffcient advection dominated accretion flows (ADAFs), with HERGs being fed by a radiatively efficient accretion mechanism.
Kinetic jet power estimates based exclusively on observed monochromatic radio luminosities are highly uncertain due to confounding variables and a lack of knowledge about some aspects of the physics of radio AGNs. I present a new methodology to calculate the jet powers of the largest, most powerful radio sources based on combinations of their size, lobe luminosity and shape of their radio spectrum. An improvement on existing models is in parametrising the magnetic field strength in the radio lobes. The derived magnetic field strengths are inconsistent with equal energy in the particles and the fields at the 5σ level. Further, I find that jet kinetic power and field strengths can be reasonably well estimated even for unresolved sources, whilst source ages require an accurate size measurement.
Numerical simulations capture complex dynamics while analytical models are good at describing synchrotron loss processes. I combine these two approaches by implementing numerical dynamics for the flow of synchrotron electron packets whilst modelling their emissivity analytically. I have developed a lossy synchrotron emissivity model which traces the evolutionary histories of individual fluid particles. The limitations of future radio surveys when measuring AGN energetics are quantifed using this model. In particular, the observed size of FR-I sources is found to depend on the survey sensitivity. At least some sources in the emerging class of FR0 objects (comprising GPS and CSS sources) can potentially be explained by a population of low-powered FR-Is.
Bright radio-loud AGNs provide an opportunity to construct standard candles detectable to high (z ⪆ 2) redshifts. I present a new technique for creating standardisable candles, based on radio-frequency observations of the most powerful AGNs; specifcally their radio flux density, lobe angular size, and radio spectrum. This technique is used to measure the distances to radio sources in the 3C and HeRGE surveys. These radio AGN standardisable candles are shown to be inconsistent with a non-accelerating universe at greater than the 6σ level, but are consistent with a flat universe. Dark energy and matter densities of Ωm = 0:289 ± 0:012 and = ΩΛ 0:711 ± 0:012 are obtained, consistent with those found from baryon acoustic oscillations, CMB measurements and JLA type 1a supernovae. I further show that this distance measure provides accurate photometric redshifts for radio AGNs based exclusively upon multi-frequency radio observations.

Item Type: Thesis - PhD
Authors/Creators:Turner, RJ
Keywords: active galactic nuclei, black holes, AGN feedback, galaxy formation, cosmology, hydrodynamical simulations
Copyright Information:

Copyright 2017 the author

Additional Information:

Chapter 2 appears to be the equivalent of a post-print version of an article published as: Turner, R. J., Shalaba, S. S., 2015. The energetics and lifetimes of local radio active galactic nuclei, Astrophysical journal, 806(1), 1-18

Chapter 3 appears to be, in part, the pre-print version (authors manuscript) of an article that has been accepted for publication in Monthly notices of the Royal Astronomical Society ( Published by Oxford University Press on behalf of the Royal Astronomical Society.

Chapter 4 appears to be, in part, the pre-print version (authors manuscript) of an article that has been accepted for publication in Monthly notices of the Royal Astronomical Society ( Published by Oxford University Press on behalf of the Royal Astronomical Society.

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